26 (1) Flashcards
The evidence found in …………….. that meant our Galaxy is not alone was one of the great scientific discoveries of the twentieth century.
1924
Scientists questioned the composition and structure of the universe as early as the ………….. century. However, with the telescopes available in earlier centuries, galaxies looked like small fuzzy patches of light that were difficult to distinguish from the ………. ………. and ………………… clouds that are part of our own Galaxy.
eighteenth
star clusters / gas-and-dust
(old scientists while analyzing the stars): All objects that were not sharp points of light were given the same name, …………., the Latin word for “clouds.” Because their precise shapes were often hard to make out and no techniques had yet been devised for measuring their distances, the nature of the ……………… was the subject of much debate.
nebulae
As early as the eighteenth century, the philosopher ……….. ………. (1724–1804) suggested that some of the nebulae might be distant systems of stars (other Milky Ways), but the evidence to support this suggestion was beyond the capabilities of the telescopes of that time.
Immanuel Kant
By the early …………. century, some nebulae had been correctly identified as star clusters, and others (such as the Orion Nebula) as gaseous nebulae.
twentieth
Most nebulae, however, looked faint and indistinct, even with the best telescopes, and their …………… remained unknown.If these nebulae were nearby, with …………… comparable to those of observable stars, they were most likely clouds of gas or groups of stars within our Galaxy.
distances
If, on the other hand, the nebulas were remote, far beyond the edge of the Galaxy, they could be other ……….. ……….. containing billions of stars.
star systems
To determine what the nebulae are, astronomers had to find a way of measuring the distances to at least some of them. When the ………..-meter (………..-inch) telescope on ……….. ……….. in Southern California went into operation, astronomers finally had the large telescope they needed to settle the controversy.
2.5 / 100
Mount Wilson
Working with the 2.5-meter telescope, ………… …………. was able to resolve individual stars in several of the brighter spiral-shaped nebulae, including M31, the great spiral in ………….
Edwin Hubble
Andromeda
Among these stars (that Edwin Hubble was able to resolve), he discovered some faint variable stars that—when he analyzed their light curves—turned out to be …………….
Here were reliable indicators that Hubble could use to measure the distances to the nebulae using the technique pioneered by Henrietta Leavitt
cepheids
After painstaking work, he estimated that the Andromeda galaxy was about 900,000 light-years away from us. At that enormous distance, it had to be a separate galaxy of stars located well outside the boundaries of the Milky Way.
Today, we know the Andromeda galaxy is actually slightly more than ………… as distant as Hubble’s first estimate, but his conclusion about its true nature remains unchanged.
twice
in the 1920s when obtaining a single photograph or spectrum of a galaxy could take a full night of tireless observing. Today, larger telescopes and ………… ………… have made this task less difficult, although observing the most distant galaxies still requires enormous effort.
electronic detectors
As it turns out, the biggest and most luminous galaxies come in one of two basic shapes:
- either they are ……….. and have spiral arms, like our own Galaxy, or
- they appear to be …………. (blimp- or cigar-shaped).
Many smaller galaxies, in contrast, have an ………. ………
- flatter
- elliptical
irregular shape
Our own Galaxy and the …………… galaxy are typical, large spiral galaxies.
They consist of a ………………… (4)
Andromeda
central bulge, a halo, a disk, and spiral arms.
We view this spiral galaxy, NGC 4565, almost exactly edge on, and from this angle, we can see the dust in the plane of the galaxy; it appears ………….. because it absorbs the light from the stars in the galaxy.
dark
About two-thirds of the nearby spiral galaxies have boxy or peanut-shaped bars of stars running through their centers (Figure 26.5). Showing great originality, astronomers call these galaxies ………. ………..
barred spirals
among the spirals, the central bulge is large and luminous, the arms are faint and tightly coiled, and bright emission nebulae and supergiant stars are inconspicuous. Hubble, who developed a system of classifying galaxies by shape, gave these galaxies the designation …………..
Galaxies at this extreme may have no clear spiral arm structure, resulting in a lens-like appearance (they are sometimes referred to as ………… …………).
Inconspicuous: not easily or quickly noticed or seen, or not attracting attention
Sa
lenticular galaxies
These galaxies seem to share as many properties with elliptical galaxies as they do with spiral galaxies
At the other extreme, the central bulge is small and the arms are loosely wound. In these ………… galaxies, luminous stars and emission nebulae are very prominent.
Sc
Our Galaxy and the Andromeda galaxy are both intermediate between the two extremes.
